I'll give a non-recommendation to Avio Power Meter. Great idea (self install crank PM), but terrible execution. Units have been out for over 18 months, and they still can't address a phantom battery drain issue. Well, they say they have with the latest firmware, but that firmware doesn't calibrate properly - you end up putting out 2000 watts. I had a unit installed for 6 months - the battery issue got so bad I was replacing the battery every other day. Last week the unit stopped working even with a new battery - icing on that cake was the battery door broke from repeated removal/install. So, I took a mallet and plastic prybar and removed the POS.
I think I'll be going with pedal based system.
John